As a method for uniformly recording or erasing an image on a thermoreversible recording medium (hereinafter, it may also be referred to as a “recording medium” or a “medium”) in case of surface irregularity on the medium or remote recording or erasing, various methods of making a laser light have been proposed (see PTL1 and so on). As such an image processing method by a laser light, a laser recording apparatus (laser marker) which enables to irradiate a high-power a laser light on the thermoreversible recording medium and control a location thereof has been provided. When the laser light is irradiated on the thermoreversible recording medium using this laser marker, a photothermal conversion material in the thermoreversible recording medium absorbs the light and converts it into heat, and image recording and image erasing can be carried out by the heat. For example, as a method for carrying out image recording and image erasing by a laser light, a method for recording by a near-infrared laser light, where a leuco dye, a reversible color developing agent, and various photothermal conversion materials are combined, has been proposed (see PTL2).
Here, examples of a method for scanning a laser light in image recording and image erasing using the laser light include those illustrated in FIG. 1 and FIG. 2. Here, in FIG. 1 and FIG. 2, solid arrows denote a laser drawing operation (marking operation), and dashed arrows denote a jump operation of moving drawing points (idling operation).
In FIG. 1, a first laser drawn line 201 is drawn from a first starting point to a first end point, and the laser light is irradiated and scanned so that a second laser drawn line 202 adjacent to the first laser drawn line 201 is drawn in parallel with the first laser drawn line 201 from a second starting point to a second end point.
According to the laser light scanning illustrated in FIG. 1, drawing in a short image recording time is possible with less speed reduction at a turnaround portion. However, due to a heat accumulation effect of printing the starting point of the second laser drawn line 202 right after printing the end point of the first laser drawn line 201, the thermoreversible recording medium is excessively heated at the turnaround portions of the laser drawn lines. As a result, there are problems of non-uniform image density and reduced repetition durability.
FIG. 2 illustrates a method for irradiating and scanning a laser light, where a first laser drawn line 211 is drawn from a first starting point to a first end point; the laser light is scanned without irradiating from the first end point to a second starting point; and a second laser drawn line 212 adjacent to the first laser drawn line 211 is drawn from the second starting point to a second end point in parallel with the first laser drawn line 211 (see PTL3).
According to this laser light scanning illustrated in FIG. 2, reduction of speed at a turnaround portion and an effect of heat accumulation may be improved, and an excess energy application on the thermoreversible recording medium may be avoided. Thereby, repetition durability improves. However, a dashed portion with no laser light irradiation is long, and thus an image recording time and an image erasing time are long. Also, in the laser light scanning method, as an alternative of reducing the heat accumulation effect, the second laser drawn line 212 is recorded in a cold state after the first laser drawn line 211 is drawn. Thus, heat accumulation cannot be used, and high energy is required. Thus, a scanning speed cannot be increased, and there is a problem that the image recording time cannot be reduced.
Also, the present applicants have proposed earlier a method for irradiating and scanning a laser light illustrated in FIG. 3 such that a first laser drawn line 221 is drawn from a first starting point to a first end point and then a second laser drawn line 222 adjacent to the first laser drawn line 221 is drawn from a second starting point toward a second end point located on a line in a direction tilted to the first starting point with respect to a line parallel to the first laser drawn line 221 (see PTL4).
According to this proposal illustrated in FIG. 3, uneven density at a solid image portion and an erased portion can be suppressed, and repetition durability of the solid image may be improved. At the same time, image printing and erasing times can be reduced. However, since the second laser drawn line 222 is diagonally recorded, there is a problem that an end portion of an image is missing depending on the types of the image.
Among images drawn by scanning a laser light, in case of drawing a bar code image in particular, a high image density and an accurate line width are required, it is necessary to draw the image by irradiating a high-energy laser light for improved readability. However, in all the methods for scanning a laser light described in the prior art, heat accumulation effect of a laser drawn line at a turnaround portion is not sufficiently resolved. Thus, it is at present difficult to draw an image with a high image density and an accurate line width and repeatedly draw an image with high readability when the image is a diagram of an arbitrary line width formed by a plurality of laser drawn lines, which requires a high image density and an accurate line width and requires improvement in readability, particularly a bar code image.